Energy transmission cables, such as electrical power cables and communication data transmission cables, are typically constructed with a substantially circular cross-section and include a solid insulating jacketing or sheath which encloses the internal components of the cable. The shape and composition of the outer surface of the sheath of the cable determines the ease with which the cable can be pushed or pulled across and in contact with another surface, such as, for example, the outer surface of the outer jacket of another cable or the inner wall surface of a passageway in which the cable is installed. Frequently, a cable is installed in a passageway, such as a duct, which contains other cables, such as optical fiber cables or electrical power cables.
The friction between a cable and another surface which the cable contacts resists movement of the cable and subjects the cable, or its internal components, to stress as the cable is moved with respect to the surface. The amount of stress that is imposed on the cable increases as the length of the cable that is subjected to friction increases. The stress on the cable generated by friction can cause damage or harm to the components of the cable. For example, if too large of a pulling force is applied to a cable during installation as a result of friction that occurs along a long length of the cable that is pulled over another surface, the cable may elongate beyond an allowable extent. This undue elongation can cause breaks or fractures in the cable that severely damage the cable jacket and internal components of the cable.
It is known to apply a lubricant to the jacket of a cable at the point and time that the cable is to be installed in a duct, or to apply a lubricant to the innermost surface of the duct in which the cable is to be installed, such as by flooding of lubricants into the duct, to reduce the friction between the respective surfaces of the cable and the duct that will contact each other during cable installation. See, for example, U.S. Pat. Nos. 3,565,213 and 4,063,617, incorporated by reference herein, which describe methods of lubricating a cable as the cable is pulled into a duct. Improper or inadequate lubrication of either the cable or the duct can result in damage to the cable when the cable is pulled against the innermost surface of the duct during or after installation at an installation site.
The application of a lubricant on a cable or a duct in which the cable is to be installed, at the time of installation, is not, however, always a simple, inexpensive and convenient procedure. For example, the environmental conditions present at the installation site may be severe. Also, the additional manpower and equipment required to apply the lubricant may be costly. Further, the entire lubricating procedure can be very time consuming.
Currently, many of the known lubricants that are applied to a cable at an installation site are made of grease, oil or gel-like material, each of which can cause a messy, heavy residue of lubricant to remain on the cable jacket. This messy residue can impede subsequent handling, and operations to obtain access to internal components of the cable, such as splicing of an optical fiber cable to access individual fibers in the cable.
U.S. Pat. No. 3,925,216, incorporated by reference herein, attempts to solve the problems that a residue on the cable jacket can cause by disclosing a lubricant which will evaporate after installation. The lubricant of the '216 patent, however, is an alcohol water solution and it is known that alcohol may potentially have an adverse effect on typical cable jacket materials, such as polyethylene and polypropylene. Additionally, it has been found that the lubricant of the '216 patent evaporates quickly, thereby requiring its application near or at the installation site, which may be inconvenient and time consuming. Further, the lubricant of the '216 patent is water soluble and, therefore, may become removed from or washed off of the cable jacket if a cable with such lubricant is installed in a duct where water has collected or collects. Consequently, over time, the lubricant that was applied to the jacket to ease the pulling of the cable may be absent from the jacket when the need for maneuvering the cable within or removing the cable from a duct arises.
U.S. Pat. No. 4,170,673, incorporated by reference herein, discloses a gel-like, semi-liquid lubricant for a cable which does not evaporate. This lubricant, however, may be messy to apply and use and, in addition, is removable with a water flush. Thus, like the lubricant of the '216 patent, if the cable has been installed in a duct in which water collects or flows, the cable subsequently may not be easily removed from or maneuvered within the duct.
U.S. Pat. Nos. 4,522,733 and 4,461,712, incorporated by reference herein, disclose substantially neutral aqueous lubricants which can be applied to cables that are to be installed in water-filled conduits. These lubricants are slow to evaporate and leave a residue on evaporation which can provide substantial lubricating properties for a substantial time after the cable is installed in a water-filled duct. These lubricants, however, are not permanent and may wear off of a cable, even before the residue itself evaporates, if the cable experiences heavy loading when it is pulled through a duct or across another cable. Further, these lubricants are most effective when still in an aqueous gel, which results in the disadvantages discussed above.
U.S. Pat. No. 4,781,847, incorporated by reference herein, discloses a lubricant which is slow to evaporate and provides effective dry lubrication, thereby appearing to solve most of the foregoing problems related to the lubricant which is applied to a cable. It has been found, however, that the lubricant of the '847 patent is not permanent and may become removed from or wear off of the jacket as a result of heavy loading on the cable during cable pulls.
Therefore, there is a need for a lubricating coating layer for a jacket of a cable which is easily provided on the cable jacket during the cable manufacturing process; is dry, non-tacky and water insoluble once a lubricant composition, from which the lubricating coating layer is formed, is applied and dried and cured on the cable; does not provide a messy residue on the cable; maintains a high degree of lubricity at the cable jacket surface for a long time after being provided on the cable, including the time subsequent to installation of the cable in a passageway; is a permanent coating which can withstand the wear associated with abrasive loadings ordinarily experienced by a cable; is nonflammable; and continues to have the above qualities after being subjected to a wide range of temperatures and to conditions of moisture.